`IO.Process.spawn` on windows insert additional quotes, leading to errors for certain kinds of commands

Prerequisites

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Description

IO.Process.spawn inserts additional unnecessary quotes, leading to problems trying to execute e.g. cmd.exe /c echo hi because the current quoting turns it into "cmd.exe" "/c" "echo" "hi", producing an error unknown command ""echo"". Avoiding unnecessary quoting should solve this issue.

Context

This came up while trying to write a test for #8534. The "solution" I used highlights another problem which is that the command string is not correctly quoted.

Steps to Reproduce

#eval return (← IO.Process.output { cmd := "cmd.exe", args := #["/c", "echo", "hi"] }).stderr

Expected behavior: The process should run successfully and produce no stderr. The output should be: "hi\r\n".

Actual behavior: The process produces an error message along the lines of unknown command ""echo"".

Versions

Lean 4.21.0-nightly-2025-05-30

Impact

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Start at the IO.Process.spawn entry point and reproduce the Windows case with IO.Process.output using cmd.exe and args #["/c", "echo", "hi"]. Compare the actual stderr with the expected "hi\r\n" and verify that the command runs without the unknown-command error. The issue mentions a test for #8534, but gives no test file path.